This invention relates to control of electrical appliances within a building, including both remote and local control. In particular, the invention relates to a system which utilizes the common power distribution lines of a building to provide a medium for communication between a central control unit and a plurality of remote slave units respectively adapted to be coupled to appliances to be controlled.
Systems of this type are disclosed, for example, in U.S. Pat. Nos. 4,174,517 and 4,200,862. Such systems typically include a central control unit and a plurality of remote slave units, each of which units includes an integrated circuit microprocessor and is adapted to be plugged into an outlet socket of the domestic electrical power main. Input means are provided on each slave unit for programming its microprocessor with a coded address for that unit and input means are provided on the central control unit for programming its microprocessor and controlling the transmission of command signals to the slave units. In this regard, the central control unit includes a transmitter/modulator and each slave unit includes a receiver/demodulator. Additionally, each slave unit may include a transmitter/modulator and the central control unit may include a receiver/ demodulator so that signals indicative of the status of the slave units may be transmitted therefrom to the central control unit.
While such prior systems have generally provided effective remote control of appliances, they have had a number of disadvantages. Thus, certain functions, such as lamp dimming control, could be performed only from the central control unit and could not be executed locally at the appliance. On the other hand, a function which could be controlled at the appliance, such as turning the appliance off at its own switch, would remove that appliance from control by the system. Furthermore, while lamp dimming functions controlled from the central control unit are provided, there is no means for instantaneously turning the lamp on to a predetermined dimmed condition. In order to bring an individual lamp to an intermediate brightness condition, it is necessary to first turn it full on and then run it manually through the dimming operation until the desired brightness level is reached.
Another drawback of the prior art systems is that they provide no means for verifying at the central unit whether a transmitted command has been executed by a slave unit. Furthermore, these systems are capable of being pre-programmed by the user with a number of commands to be automatically executed at predetermined times. The system then automatically transmits the programmed commands at the appointed times. But once a set of commands is loaded into the system memory, there is no means provided for testing the user-entered program to make sure that the commands have been properly stored in the system memory and to verify that they can be properly executed by the system. The only way to determine a defect in the program is to constantly monitor the system until the entire program has been completed and see if it was properly carried out.